Hobby servo motor linear actuator systems

ABSTRACT

Hobby servo motor linear actuator systems are provided. In certain circumstances, a linear actuator system includes a lead screw attachment mechanism and a lead nut. The lead screw attachment mechanism is configured to be rotatably connected to an output shaft of a hobby servo motor assembly. The lead nut is configured to move linearly along the lead screw attachment mechanism as it is rotated. The system is optionally either open-looped or closed-loop. The lead screw attachment mechanism has an outer surface that can include multiple different types of threads such as, but not limited to, gear teeth and screw threads. The hobby servo motor assembly may include one hobby servo motor or multiple hobby servo motors that work together.

BACKGROUND

A servo motor (a.k.a. simply a “servo”) is a device having a rotatableoutput shaft. The output shaft can typically be positioned to specificangular positions in accordance with a coded signal received by theservo. It is common that a particular angular position will bemaintained as long as a corresponding coded signal exists on an inputline. If the coded signal changes, the angular position of the shaftwill change accordingly. Control circuits and a potentiometer aretypically included within the servo motor casing and are functionallyconnected to the output shaft. Through the potentiometer (e.g. avariable resistor), the control circuitry is able to monitor the angleof the output shaft. If the shaft is at the correct angle, the motoractuates no further changes. If the shaft is not at the correct angle,the motor is actuated in an appropriate direction until the angle iscorrect.

There are different types of servos that include output shafts havingvarying rotational and torque capabilities. For example, the rotationaland/or torque capability of an industrial servo is typically lessrestricted than that of a hobby servo. That being said, hobby servos aregenerally available commercially at a cost that is much less than thatassociated with industrial servos.

Because hobby servos are relatively small and inexpensive, they arepopular within the hobby-mechanical industry for applications such as,but by no means limited to, hobby robotic applications andradio-controlled models (cars, planes, boats, etc.). One example of ahobby servo is the Futaba S-148 available from Futaba Corporation ofAmerica located in Schaumburg, Ill.

SUMMARY

An aspect of the disclosure relates to hobby servo motor linear actuatorsystems. In certain circumstances, a linear actuator system includes alead screw attachment mechanism and a lead nut. The lead screwattachment mechanism is configured to be rotatably connected to anoutput shaft of a hobby servo motor assembly. The lead nut is configuredto move linearly along the lead screw attachment mechanism as it isrotated. The system is optionally either open-looped or closed-loop. Thelead screw attachment mechanism has an outer surface that can includemultiple different types of threads such as, but not limited to, gearteeth and screw threads. The hobby servo motor assembly may include onehobby servo motor or multiple hobby servo motors that work together.These and other features are discussed below and shown in theaccompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a linear actuator system with a leadnut.

FIG. 2 is a schematic drawing of a linear actuator system with a slidingtube and a fixed cover.

FIG. 3 is a perspective view of a multiple motor drive mechanism with anouter casing removed to show the multiple motors.

FIG. 4 is a perspective view of a multiple motor drive mechanism with anouter casing.

FIGS. 5-1, 5-2, and 5-3 are perspective views of a hobby servo motor.

FIG. 6 is a side view of a lead screw attachment mechanism that includesan outer surface having multiple different types of threading.

FIG. 7 is a side view that shows internal components of the lead screwattachment mechanism shown in FIG. 6.

FIG. 8 is a perspective view of a lead screw attachment mechanismattached to a hobby servo motor.

DETAILED DESCRIPTION

FIG. 1 is a schematic drawing of one example of a linear actuator system100. System 100 optionally includes a motor 102, a lead screw attachmentmechanism 106, a lead nut 108, and a feedback mechanism 110. Motor 102illustratively has a rotatable output shaft 104, and motor 102 may bepart of either an open-loop system or a closed-loop system. In anopen-loop system, the position, direction of rotation, and/or speed ofrotation of output shaft 104 are based on an operator input 114 withoutany feedback. In a closed-loop system, the position, direction ofrotation, and/or speed of rotation of output shaft 104 are based on bothan operator input 114 and feedback 112 from feedback mechanism 110.

The output shaft 104 illustratively has a number of splined features,and the attachment mechanism 106 has an inner surface 116 that isconfigured to functionally engage the splined features such thatrotation of output shaft 104 is transferred to attachment mechanism 106.Accordingly, output shaft 104 and attachment mechanism 106 are in-linewith each other and rotate about a same axis of rotation 118.

In an embodiment, the outer surface of attachment mechanism 106 hasmultiple different textured surfaces. For example, the outer surface ofattachment mechanism 106 may have two or more threaded surface. In theparticular example shown in FIG. 1, attachment mechanism 106 has a lowerthreaded section 120 and an upper threaded section 122. The lowersection 120 may have gear-teeth type threading, and upper section 122may have screw type threading. In other embodiments, only one ofsections 120 or 122 may have threading, and the other section has asmooth outer surface. Embodiments are not however limited to anyconfiguration.

Lead nut 108 illustratively has an inner surface 124 that has threadingthat corresponds to the threading of upper section 122. For instance,inner surface 124 may have screw type threading that enables lead nut108 to be able to move up and down along lead screw attachment mechanism106 in a screw and nut type fashion. In one embodiment, lead nut 108 isprevented from rotating while lead screw attachment 106 is rotated. Thisresults in lead nut 108 moving up and down along the attachmentmechanism 106 in the directions shown by arrow 128. Accordingly, system100 is able to turn rotational movement 126 of lead screw attachmentmechanism 106 into linear motion 128 of the lead nut 108.

In some, but not all embodiments, feedback mechanism 110 is rotatablyconnected to surface 120 of attachment mechanism 106 such that rotationof mechanism 106 is directly translated to rotation 130 of mechanism 110about axis of rotation 132. Axis 132 is optionally parallel to axis ofrotation 118 of mechanism 106. The rotation may be translated throughgear teeth on the outer surface of feedback mechanism 110 thatcorrespond to gear teeth on the surface 120. In one example of such anembodiment, feedback mechanism 110 comprises a potentiometer. In otherembodiments, feedback mechanism 110 comprises an encoder such as, butnot limited to, a magnetic encoder, an optical encoder, a rotaryencoder, or a linear encoder.

FIG. 2 is a schematic drawing of another example of a linear actuatorsystem 200. System 200 optionally includes a motor 202 (e.g. a hobbyservo motor), a lead screw attachment mechanism 206, a lead nut 208, afixed cover 252, and a sliding tube 254. The lead screw attachmentmechanism 206 optionally includes a threaded lower section 220 and athreaded upper section 222.

In an embodiment, lead screw attachment mechanism 206 is rotated aboutan axis of rotation 218 by an output shaft of motor 202. The lead nut208 is prevented from rotating by the fixed cover 252 and the slidingtube 254. Fixed cover 252 is illustratively stationary (i.e. does notmove relative to motor 202). Sliding tube 254 is able to move in thelinear directions 228, but is not able to rotate about axis 218.Accordingly, as mechanism 206 is rotated, lead nut 208 and the attachedsliding tube 254 are able to move up and down in the linear directionsshown by arrows 228.

System 200 may be either a closed-loop system or an open-loop system. Inthe case of a closed-loop system, system 200 may include a feedbackmechanism in a number of different places. In one embodiment, feedbackmechanism 210 is configured such that it does not move linearly withlead nut 208. For instance, feedback mechanism 210 may include apotentiometer or encoder that is rotated by the lower threaded section220. In another embodiment, feedback mechanism 211 is configured suchthat it does move linearly with lead nut 208. For instance, feedbackmechanism 211 may include an optical or magnetic sensor that determinesits position relative to fixed cover 252. Furthermore, in yet anotherembodiment, a feedback mechanism 212 may be included within motor 202(e.g. within a casing of motor 202) such that it is not exposed to othercomponents, and perhaps provides a cleaner appearance. Embodiments arenot limited to any particular configuration and can include any numberof feedback mechanisms including none in the case of an open-loopsystem.

FIG. 3 shows a perspective view of a multi-motor drive mechanism 300. Incertain embodiments of the present disclosure, a multi-motor drivemechanism 300 is used to rotate a lead screw attachment mechanism (e.g.mechanism 106 in FIG. 1 or mechanism 206 in FIG. 2). In other words, themotor 102 in FIG. 1 and motor 202 in FIG. 2 do not necessarily need tobe single motor systems. Instead, the motors in those figures can bereplaced with a multi-motor drive mechanism. Additionally, multi-motordrive mechanisms can be used by themselves without being incorporated ina linear actuator system.

Multi-motor drive mechanism 300 in FIG. 3 illustratively includes twomotors (e.g. two hobby servo motors) 301 and 302. Embodiments are nothowever limited to any specific number of motors and can include morethan the illustrated two (e.g. 3, 4, 5, 6, etc.). The two motors aresecured within a mounting bracket 304. Bracket 304 optionally includestwo apertures 306 and 308 that are configured to receive motors 301/302and secure them to the bracket 304.

Bracket 304 is also configured to support a rotatably mounted gear 310.Gear 310 is functionally engaged with two gears 312 and 314. Gears 312and 314 are illustratively configured to fit around a splined outputshaft of motors 301 and 302. However, in another embodiment, system 300does not include gears 312 and 314, and instead the output shafts ofmotors 301 and 302 are used directly to rotate gear 310.

In one embodiment, gears 312 and 314 have smaller outer circumferences(i.e. smaller diameters) than gear 310. In such a configuration, gear310 is able to provide a greater amount of torque than could motors 301and 302 by themselves. Embodiments are again not limited to anyparticular configuration, and gears 310, 312, and 314 could havedifferent relative sizes.

Gear 310 is illustratively attached to an attachment hub 316 thatdirectly translates rotation from gear 310. Hub 316 includes a centeraperture 317 that is surrounded by a number of satellite apertures 318.Center aperture 317 may be the same size, larger, or smaller thansatellite apertures 318. This may be beneficial in that it provides manydifferent options for attaching other components to hub 316. Forinstance, a same or similar center and satellite aperture pattern can berepeated on other components such that all of the components can beconnected together. Furthermore, bracket 304 may include one or moreattachment posts 320 that can be used to secure the components shown inFIG. 3 within an outer casing.

FIG. 4 shows a perspective view of a multi-motor drive mechanism withina casing 300. The casing includes a bottom portion 352 and a top portion354. Portions 352 and 354 illustratively support and protect thecomponents shown in FIG. 3 (e.g. the motors 301/302, gears 310/312/314,etc.). In an embodiment, top casing portion 354 includes a number ofapertures and securing mechanisms (e.g. screws) that are used to securethe mounting bracket 304 and/or posts 320 shown in FIG. 3 to the outercasing. The top casing portion 354 may also include a number ofapertures 358 that can be used to secure the multi-motor drive mechanism300 within an operating environment. FIG. 4 further shows that system300 may include one group of wires 360 that are used to provide controlsignals, power, etc. to the components within system 300 (e.g. motors301 and 302).

FIG. 5-1 is a perspective view of a hobby servo motor 500, and FIG. 5-2is a side view of hobby servo motor 500. In an embodiment, servo motor500 includes a feedback mechanism (e.g. feedback 110 in FIG. 1) and is amotor such as motor 102 in FIG. 1. Servo 500 includes attachment flanges504. Flanges 504 optionally include apertures 505 formed therein forreceiving an attachment mechanism (e.g., a screw, bolt, etc). Theattachment mechanism is illustratively utilized to secure servo 500within an operative environment. Servo 500 also includes an electricalconnection 506 that enables the servo to receive electrical power and/orcontrol signals.

Servo 500 includes a rotatable output shaft 502 also known as a servospline or a servo splined output shaft. Shaft 502 optionally has anouter perimeter or periphery that has splines or teeth. It is common forshaft 502 to have a 23, 24 or 25 tooth configuration.

Output shaft 502 is positioned to specific angular positions inaccordance with a coded input signal received by the servo. It is commonthat a particular angular position will be maintained as long as acorresponding coded signal exists on an input line. If the coded signalchanges, the angular position of the servo output shaft 502 will changeaccordingly.

In an embodiment, output shaft 502 includes a threaded orifice 522.Threaded orifice 522 extends into splined output shaft 502 from itsdistal end. Orifice 522 is illustratively used to secure an item such asa gear, horn, or other attachment mechanism to shaft 502. Servo 500further includes a planar or relatively planar surface 521 thatsurrounds shaft 502. In accordance with one aspect of the presentdisclosure, gears, horn, and attachment mechanisms that are attached to,rotatably coupled to, or functionally engaged to shaft 502 also includea planar or relatively planar surface. In such an embodiment, a surfaceof the item being attached and surface 521 are engaged to one another ina relatively flush relationship.

FIG. 5-3 is a perspective view of hobby servo motor 500 showing aninternal potentiometer 552 and control circuit 550 removed from thehobby servo housing or casing. Control circuit or circuits such ascircuit 550 and an internal potentiometer such as potentiometer 552 arecommonly included within the housing or casing of a hobby servo motor.The control circuitry and potentiometer are functionally connected tothe hobby servo motor rotatable output shaft. Through the potentiometer(e.g., a variable resistor), the control circuitry is able to monitorthe angle of the output shaft. If the shaft is at the correct angle, themotor actuates no further changes. If the shaft is not at the correctangle, the motor is actuated in an appropriate direction until the angleis correct. In an embodiment, internal potentiometer 552 is replacedwith a feedback mechanism (e.g. mechanism 110 in FIG. 1). In at leastcertain circumstances, the new feedback mechanism includes an internalencoder that enables output shaft 522 to perform multiple rotations(e.g. 720 degrees, 1080 degrees, etc.). Additionally, it should bementioned that in certain embodiments, motor 500 comes preconfiguredwith an internal encoder and does not need to be modified.

Rotation of a servo output shaft such as shaft 502 is typically limitedto around 180 degrees. In most cases, rotation is limited at leastbecause of an internal mechanical stop. It is also common that servooutput shaft 502 is capable of producing a relatively limited amount oftorque power. The torque and rotational limitations of a hobby servo areadequate for many applications; however, some applications require aservo having torque power and/or a rotational capacity that is beyondthe capability of a typical hobby servo. Increased torque power and/orrotational capacity enable greater mechanical flexibility.

In accordance with one embodiment of the present disclosure, hobby servomotors such as servo 500 are internally modified to enable a range ofoutput shaft rotation that is greater than its “off-the-shelf”capability. For example, in accordance with one embodiment, an internalmechanical stopping mechanism, which prevents rotation past apredetermined angle, is removed from hobby servo motor to enable forcontinuous rotation in either direction. As a result of themodification, the rotatable output shaft of a hacked or modified servois able to rotate beyond the range of rotation prior to themodification.

Following modification of servo 500, limitations inherent to theinternal potentiometer make it a poor choice for subsequent controlfunctionality. As previously mentioned, in a normal servo operatingconfiguration, the servo motor rotates the servo output shaftcorresponding to the coded signal received by the servo. The outputshaft is rotated until the signal from the internal potentiometer of theservo, which corresponds to the angular position of the servo outputshaft, matches the coded signal received by the servo. Most hobby servoscontain internal potentiometers such as potentiometer 552 shown in FIG.5-3 that are physically limited to monitoring a limited range of angles(e.g., often less than 200 degrees). Therefore, when a servo 500 ismodified for extended rotation, the internal potentiometer is not thebest control component for applications that require the servo shaft torotate beyond the typical rotation limits in order to provide improvedrotational capacity. The internal potentiometer is not likely to supportcontrol of a range of rotation that is even equivalent to the originalrotational range of the servo output shaft.

In accordance with one aspect of the present disclosure, the internalpotentiometer is disconnected and an external/auxiliary potentiometer isinserted into the control scheme to facilitate proportional control ofthe servo splined output shaft. Alternatively or in addition, theinternal potentiometer is optionally replaced with a feedback mechanism(e.g. mechanism 110 in FIG. 1). In an embodiment, servo 500 utilizes thecoded input signal and the signal from an external potentiometer torotate and position the output shaft. A particular externalpotentiometer having any of a variety of control characteristics can beselected and implemented based on the requirements of a givenapplication. Therefore, a potentiometer with a rotational range ofsubstantially less than or greater than 180 degrees can be selected andimplemented as desired.

FIG. 6 is a side view of a lead screw attachment mechanism 606.Attachment mechanism 606 illustratively includes a top surface 602, abottom surface 604, and an output shaft attachment housing 1308.Additionally, mechanism 606 optionally includes two or more differentsurfaces along the rotatable shaft. In the embodiment shown in FIG. 6,mechanism 606 includes a first threaded surface 620 and a secondthreaded surface 622. First threaded surface 620 may for instanceinclude screw, worm screw, gear, or any other type of threading. Secondsurface 622 may also illustratively include screw, gear, or any othertype of threading. In one embodiment, first and second threaded surfaces620 and 622 include different types of threading (e.g. one includesscrew threading and the other gear threading), or alternatively, bothsurfaces 620 and 622 may include the same type of threading. In anotherembodiment, one or more of surfaces 620 or 622 may instead include anon-textured surface (e.g. a smooth outer surface such as that shown inFIG. 8). Additionally, embodiments of mechanism 606 are not limited toonly including two surfaces along the rotatable shaft. Embodiments ofmechanism 606 optionally include any number of surfaces along therotatable shaft. For instance, mechanism 606 may include three differentsurfaces instead of the two shown in FIG. 6 with one surface havingscrew threading, one gear threading, and the other surface being smooth.

FIG. 7 is a side view of lead screw attachment mechanism 606 thathighlights internal features with dotted lines. Mechanism 606 includestop surface 602, attachment mechanism orifice 610, attachment surface607, output shaft attachment housing 608, top receiving surface 614,spline receiving surface 612, and bottom surface 604. Embodiments ofmechanism 606 include any desired dimensions. Embodiments of mechanism606 are made from every material. Examples of materials include rigidmaterials such as 6061 T6 aluminum.

FIG. 8 is a perspective view of an embodiment of a lead screw attachmentmechanism 806 attached to an exemplary hobby servo 802. The particularembodiment of mechanism 806 includes a smooth outer surface 800. Inother embodiments, outer surface 800 includes one or more texturedportions as is shown in the previous drawings. Mechanism 806 is securelyand functionally engaged to a motor rotatable output shaft, andmechanism 806 bottom surfaces 604 and/or 652 (shown and labeled in FIG.7) are flushly engaged with a circular planar surface of the motor. Inan embodiment, mechanism 806 is securely attached to hobby servo 802using screw 804. In other embodiments, attachment mechanisms other thanscrews are used. The attachment of mechanism 806 to hobby servo 802provides many useful features. Mechanism 806 provides enhancedperformance such as increased strength and durability. Mechanism 806supports greater side-loads on the servo than the servo could supportalone. Mechanism 806 also allows for items that cannot be directlyattached to a hobby servo to be indirectly attached.

Finally, it is to be understood that even though numerouscharacteristics and advantages of various embodiments have been setforth in the foregoing description, together with details of thestructure and function of various embodiments, this detailed descriptionis illustrative only, and changes may be made in detail, especially inmatters of structure and arrangements of parts within the principles ofthe present disclosure to the full extent indicated by the broad generalmeaning of the terms in which the appended claims are expressed. Inaddition, although the embodiments described herein are directed tohobby servo motors, it will be appreciated by those skilled in the artthat the teachings of the disclosure can be applied to other types ofcomponents, without departing from the scope and spirit of thedisclosure. Also, it should be noted that embodiments of the presentdisclosure illustratively include any one or more features described inthis specification or shown in the figures.

What is claimed is:
 1. A linear actuator system comprising: a lead screwattachment mechanism that is configured to be rotatably connected to anoutput shaft of a hobby servo motor assembly; and a lead nut that isconfigured to move linearly along the lead screw attachment mechanism asit is rotated.
 2. The system of claim 1, and further comprising: afeedback mechanism.
 3. The system of claim 2, wherein the feedbackmechanism is configured to move linearly along with the lead nut.
 4. Thesystem of claim 2, wherein the feedback mechanism is configured suchthat it does not move linearly along with the lead nut.
 5. The system ofclaim 1, wherein the lead screw attachment mechanism has an outersurface with multiple different types of threads.
 6. The system of claim5, wherein one of the multiple different types of threads includes screwthreads.
 7. The system of claim 5, wherein one of the multiple differenttypes of threads includes gear teeth.
 8. The system of claim 1, whereinthe hobby servo motor assembly includes one hobby servo motor.
 9. Thesystem of claim 1, wherein the hobby servo motor assembly includesmultiple hobby servo motors that are mounted together in a casing, andthat rotate a single attachment hub.
 10. A linear actuator systemcomprising: at least one hobby servo motor having an output shaft; anattachment mechanism rotatably connected to the output shaft; and a leadnut that moves linearly along the output shaft.
 11. The system of claim10, wherein the at least one hobby servo motor comprises multiple hobbyservo motors.
 12. The system of claim 11, wherein the multiple hobbyservo motors rotate a single attachment hub.
 13. The system of claim 10,wherein the attachment mechanism and the output shaft rotate about asame axis of rotation.
 14. The system of claim 10, wherein the system isan open-loop system
 15. The system of claim 10, wherein the system is aclosed-loop system.
 16. The system of claim 10, wherein the attachmentmechanism has an outer surface that includes multiple different threads.17. A linear actuator assembly comprising: a lead screw attachmentmechanism having an outer surface, a first portion of the outer surfacehaving a first type of threading, and a second portion of the outersurface having a second type of threading; and a feedback mechanism thatis configured to functionally engage the lead screw attachment mechanismutilizing the first type of threading.
 18. The assembly of claim 17,wherein the first type of threading is gear teeth, and wherein thesecond type of threading is screw threading.
 19. The assembly of claim17, wherein the lead screw attachment is rotated utilizing multiplehobby servo motors.
 20. The assembly of claim 17, wherein the feedbackmechanism is an encoder.